Insight into control of epidermal proliferation is important for understanding both skin homeostasis and disease. Uncontrolled epidermal proliferation characterizes the 2 most common cancers in the U.S., including epidermal squamous cell carcinoma (SCC). Functionally characterizing the role of identified signaling pathways and basement membrane proteins in normal human skin tissue and in epidermis undergoing progression from pre-neoplasia towards cancer using new skin models is a focus of this AR43799 competing renewal. First, we plan to characterize the function of downstream components of the Ras/MAPK cascade in human skin tissue. We will first determine if Ras-mediated control of proliferation and progression from pre-neoplasia proceeds down the classical Ras/Erk MAPK cascade by studying the necessity and sufficiency of Erk1 (p44ERK1) and Erk2 (p42ERK2) in this process. To characterize how the Ras/MAPK pathway controls cell cycle progression in human epidermis, we will define the role of Ras/MAPK-targeted cell cycle regulators that act in both G1/S and G2/M phases of the cell cycle, with a special focus on the newly identified role of Erk-induced CDC25C activation in G2/M cell cycle progression. These studies are designed to extend characterization of Ras/MAPK cascade regulation of human epidermal proliferation to downstream levels that include Erk MAPKs and their cell cycle targets. Second, we plan to define the role of specific epidermal basement membrane proteins in homeostasis and in Ras-driven progression from pre-neoplasia. We will determine if recently identified invasion-promoting sequences of collagen VII mediate binding to laminin 332 (laminin-5) and normal epidermal adhesion. We will also characterize the role of the 21 integrin subunit in proliferation and in epidermal tumor progression. To do this, we will begin by characterizing the 1 integrin subunits and stromal ligands involved in this process. These studies are designed to elucidate mechanisms of basement membrane protein function in epidermal homeostasis and in progression towards neoplasia. At the end of the proposed funding period, we hope to have characterized Ras-driven mechanisms regulating epidermal homeostasis, proliferation and the progression of human epidermis towards neoplasia. PUBLIC HEALTH RELEVANCE: Control of cell proliferation in the skin and other tissues is critical for normal body maintenance and avoidance of disease, including cancer. New approaches to study the regulatory pathways controlling proliferation in human skin tissue have identified a dominant role for the Ras/MAPK signaling pathway in normal and pathological epidermal proliferation. A deeper analysis of how this pathway regulates the cell division cycle and how it interacts with signals coming from the cell surface and extracellular space is designed to shed light on normal and pathologic control of proliferation in skin.